Monday, 3 September 2012

Marksman Electronic Tester - Teardown

Here is a quick 'teardown' of the "Marksman Multi-Function Electronic Tester" available on eBay for a few quid. It promises to do pretty much everything! I bought it as a cheapo NC voltage detector - I don't really know why, it wasn't going to be an improvement on my Fluke. I did like the idea of its continuity testing feature though.

Here it is in its original packaging. Exciting stuff. Free batteries!

Here it is as a size comparison with a Fluke VoltAlert 1AC-E II. It's a little bit thinner, but squarer. The yellow cap on the Marksman is just a cover. It unclips to reveal a metal screwdriver tip for poking stuff.

Here's the "instructions". I especially like: "The perceptibility of the indication can be impaired......on wooden runged ladders etc"

Here's it disassembled. The board is soldered on to the screwdriver tip with a bit of uninsulated solid wire. The cover is glued on (you can see the blue bits of stuck plastic on the yellow top cover.

Now here's where it starts to get interesting; and the reason I took it apart in the first place. These are the legs of the PCB mounted slide switch to toggle the sensitivity. Red lines are showing solder/track joins, two circles for the switch casing solder tags.

I couldn't get it to be any more/less sensitive - it was either in contact mode, or non-contact mode. Red light, or green light. Anyway, I drew the schematic out to see exactly what was going on -->
As you can see, there is nothing at all variable, both of the switch positions for Non-contact mode connect the exact same pins!

For the rest of it, there's a darlington pair and a couple of resistors with the red LED, and a 4069 CMOS hex inverter for the Green. Two gates to detect, two as an oscillator to make the speaker go BEEEEEEEEEEP (a little under 4KHz with those component values if you were wondering)

Just to make it even more clear, here is the pinout config of the switch (but upside down compared to the photo above). Pos 1 = Contact RED led mode, Pos 2,3 GREEN led mode, soldered together on the PCB.

Maybe I got a fake one or something, maybe it is just typical Chinese crappy electronics that shouldn't be allowed to be sold.